1. Field of the Invention
The present invention relates to a cantilever chip for a scanning probe microscope.
2. Description of the Related Art
By using element techniques such as a servo technique in a scanning tunneling microscope (STM) devised by Binnig and Rohrer et al., a microscope allows observation of an insulating sample, which is not easily measured by the STM, at accuracy of an atomic order. As this microscope, an atomic force microscope (AFM) is proposed and practically used.
The AFM is similar to the STM in structure, and the AFM is classified as one of the scanning probe microscopes. In the AFM, a cantilever having a sharp projection portion (probe portion) at its free end is brought close to a sample, the motion of the cantilever which is displaced by interaction acting between atoms of the distal end of the probe and atoms of the sample surface is electrically or optically measured while the probe portion relatively moves along the sample surface, and data of the respective points of the sample surface are time-serially detected and processed, thereby obtaining three-dimensional data such as unevenness data of the sample.
Conventionally, as a cantilever for a scanning probe microscope, an SiO.sub.2 cantilever chip formed by applying a semiconductor IC process is proposed in "Thomas R. Albrecht and Calvin F. Quate, "Atomic resolution Imaging of a nonconductor by Atomic force Microscopy" J. Appl. Pys, 62(1987)2599". Since this proposal, cantilevers are easily formed at high accuracy in a micron order with good reproducibility, and are manufactured at low cost by using a batch process. For this reason, cantilevers formed by applying the semiconductor IC manufacturing process are popularly used.
For example, a cantilever chip which is described in "J. Vac. Sci. Technol. A8(4)3386 1990 (T. Albrecht, S. Akamine, T. E. Caver and C. F. Quate)" and in which, in place of an SiO.sub.2 film, a silicon nitride film is used as a cantilever constituent material has been commercially available. This cantilever has a length of about 50 to 200 .mu.m, a thickness of about 0.5 to 1 .mu.m, and a shape of a hollow triangle or rectangle.
When the cantilever chip is to be mounted on an AFM apparatus, the cantilever chip is inclined on the apparatus at an angle of about 15.degree. with respect to the sample such that the support portion of the cantilever is not brought into contact with a target sample. In a cantilever manufactured in a normal batch process, the axis of the probe at the distal end of the cantilever is perpendicular to the surface of the cantilever. For this reason, the axis of the probe is not parallel to a normal extending from the surface of the target sample, and the probe opposes the normal while the probe is inclined. In this state, when AFM measurement is performed, and the sample has a step portion, the side surface of the probe may collide against the upper end of the step portion on one of the rising and falling sides of the step portion before the distal end of the probe reaches the lower end of the step portion. For this reason, when a grating sample having a large number of rectangular grooves crossing the scanning direction of the probe is measured, although both sides of each of the grooves have the same shape, measurement results, i.e., traces of the distal end of the probe are different from each other, and an image which does not accurately represent the surface shape of the sample is obtained.
In addition, the resolving powers of a scanning probe microscope in the horizontal and vertical directions depend on a degree of sharpness of the probe. For this reason, a probe having a sharp distal end is desirably used.